120 SOME PRACTICAL LESSONS FROM SOIL BACTERIOLOGY. 



method should always be tried. Soil from some locality where the 

 legume grows luxuriantly should be imported and mixed with the 

 field which is to be planted with the legume. But one should be 

 careful that the inoculating soil does not bring troublesome weeds or 

 plant diseases. In using either the earth inoculations or pure 

 cultures, it must be borne in mind that if a soil is already well stocked 

 with the tubercle bacteria, inoculations are not likely to do any good; 

 but in soils where a new legume is to be grown or where the legume 

 to be planted does not flourish, soil inoculation may be of decided 

 advantage. 



Soil Inoculation with Manure. Manure is added to the soil 

 primarily as a means of furnishing plant food; but it has become 

 evident that the inoculation of the soil with the immense amount of 

 bacteria in the manure is in itself of extreme value, sometimes, as in 

 pasture soil, of more value than the actual food substances in the 

 manure. The use of manure upon the soil must, therefore, be 

 looked upon as one of the very useful methods of inoculating the 

 soil with the bacteria needed to carry out the soil transformations. 



CONTROL AND STIMULATION OF SOIL BACTERIA. 



It has become more and more evident, as information has ac- 

 cumulated, that a vigorous activity of the bacteria found in the soil 

 is needed to carry out the various transformations of plant foods. 

 These bacteria are commonly abundant enough; and sometimes 

 they find the conditions so favorable that they grow rapidly, pro- 

 ducing vigorous actions; but at other times the conditions in the 

 soil are unfavorable, and they are held in check. What is chiefly 

 needed, then, in the treatment of soil is, not the inoculation of more 

 bacteria, but a modification of the soil conditions so as to favor the 

 growth of those already there. While this is a complicated sub- 

 ject and one that will require different treatment in different cases, 

 a few general principles may be formulated. 



Acidity. Most bacteria, and practically all the useful bacteria, 

 are very sensitive to the presence of acid, failing to grow at all in 

 an acid medium. If the soil is but slightly acid, bacterial agencies 



